Lighting systems for passenger seating areas in mass-transit vehicles frequently include a plurality of fluorescent lamps arranged in rows. Each row of lamps is commonly enclosed within an elongated channel that forms part of an elongated lamp housing. The elongated channel may be connected to or integrally formed with an elongated display panel for holding advertising cards. A lamp housing of this type will also typically include an elongated translucent or transparent light cover disposed across the open side of the channel to aid in controlling the distribution of light emitted from the lamps.
Together, the lamp housing and display panel make up an elongated light fixture. Such light fixtures are typically manufactured in long sections that mount end-to-end in the cornice areas above the passenger seating areas and above the vehicle side windows in mass-transit vehicles. U.S. Pat. No. 4,574,336 issued Mar. 4, 1986 to Mikalonis and U.S. Pat. No. 4,387,415 issued Jun. 7, 1983 to Domas disclose lighting systems of this type.
Fluorescent vehicle lighting systems are inherently difficult to service and require a considerable amount of maintenance. Fluorescent lamps frequently burn out and require replacement. When lighting systems use large numbers of lamps, the odds that one of the lamps will burn out over a given period of time increases. Therefore, the larger the number of lamps that a lighting systems uses, the more often that system will require bulb and ballast replacement.
Lighting systems that use multiple lamps also require multiple lamp sockets and complex wiring harnesses. Wiring harnesses for multiple-lamp lighting systems must connect every lamp socket to an electrical power source. In addition, the lighting fixtures housing the lamps and ballast must be designed to allow easy access for the purpose of replacing lamps and ballast.
Systems using multiple lamps inherently leave "dark spots" between lamps. Rows of fluorescent lamps oriented end-to-end leave dark spots where the ends of each lamp plug into a socket and no light is emitted. The dark areas between the lamps are difficult to minimize without extending the lengths of the lamps.
When confronted with applications requiring linear light sources, designers have sometimes turned to fiber optics. Advances in fiber optic technology have made it possible to manufacture linear light sources that can efficiently distribute light both laterally from their circumferences as well as longitudinally from their ends. This type of product is known as a "side-light" or "side-fire" optic or a "side-fire" light pipe.
Lumenyte International Corporation manufactures a "side-fire" light pipe that includes a solid acrylic core with either a circular or an oval cross-section. The diameter of the core is approximately one-half of an inch. A Teflon.RTM. cladding surrounds the core and has an index of refraction that causes the light pipe to emit light laterally. A clear jacket surrounds the cladding to reflect a certain amount of light back into the core.
Also available from Lumenyte International Corporation is the LUMENYTE.RTM. STARBURST.TM. OPTIC--a side-fire light pipe with small angled cuts along its length. The cuts create optical discontinuities along the length of the light pipe that increase the amount of light emitted laterally. The depth, angle and spacing of these cuts can be varied to customize light distribution to suit a particular application.
The prior art also includes fiber optic lighting systems that have been proposed for use in vehicular applications. An example of a proposed vehicular application of fiber optic technology is described in U.S. Pat. No. 4,947,293 issued to Johnson et al. The Johnson et al. patent discloses a clearance lighting system for a semi trailer cargo container body. The system includes a light source that end-illuminates elongated light-conducting strips. The strips are supported along both sides of a container body and emit light both longitudinally and laterally. Another Johnson patent, U.S. Pat. No. 5,122,933, discloses a similar fiber optic lighting system that includes a message panel. However, the lighting systems disclosed in the later two patents are not adapted to preferentially distribute light into the passenger seating area of a mass transit vehicle.
Another example of a vehicular application for fiber optic technology is disclosed in U.S. Pat. No. 4,740,870 issued to Moore et al. The Moore et al. patent discloses a fiber optic lighting system for boats. The system includes a plurality of "end-fire" fiber optic cables that each receive light at one end from a central light source. The cables conduct light longitudinally to light fixtures located at remote locations within a boat.
Two other examples are disclosed in U.S. Pat. No. 4,811,172 to Davenport et al. and U.S. Pat. No. 5,184,883 to Finch et al. Each of these patents discloses a fiber optic lighting system for motor vehicles. The systems include a light source that end-illuminates a plurality of fiber optic filaments. The filaments conduct the light longitudinally to the vehicle head and tail lamp fixtures.
There remains a need for lighting systems that can supply sufficient illumination to meet lighting requirements in passenger seating areas of mass-transit vehicles while reducing the amount of lamps, wiring and maintenance that current systems require.